The body of a government soldier lay in the street outside the military headquarters and a column of smoke billowed into the sky from inside the compound, sending panicked residents running through the streets.

It was not immediately clear what started the fighting but it did not appear to be a confrontation between government forces and rebels. Clashes between those two factions have largely been fought in other region’s of the country.

The UN Security Council on Tuesday voted unanimously to almost double the number of peacekeepers to 12,500.

Earlier President Salva Kiir said his forces had recaptured the key town of Bor days after it was seized by rebels.

The rebels are led by Riek Machar, of the ethnic Nuer, who has been battling President Kiir, of the Dinka.

The UN also said on Tuesday that it had reports of at least three mass graves.

One was in Bentiu in the north, and two in the capital, Juba.

In a Christmas message, Mr Kiir said “innocent people have been wantonly killed”, adding: “There are now people who are targeting others because of their tribal affiliation. It will only lead to one thing and that is to turn this new nation into chaos.”

‘Palpable fear’

Mr Lanzer told the BBC’s Newshour programme: “I think it’s undeniable at this stage that there must have been thousands of people who have lost their lives.

“When I’ve looked at the hospitals in key towns and I’ve looked at the hospitals in the capital itself, the range of injuries, this is no longer a situation where we can merely say it’s hundreds of people who’ve lost their lives.”

Mr Lanzer also said that the number of people seeking shelter from the fighting was “tens of thousands if not hundreds of thousands”.

He said that the tensions between different communities in South Sudan was even evident within a UN base he had just visited where some 7,500 people are seeking protection.

The UN High Commissioner for Human Rights, Navi Pillay, said: “There is a palpable fear among civilians of both Dinka and Nuer backgrounds that they will be killed on the basis of their ethnicity.”

The UN says at least 80,000 people have been displaced by the South Sudan crisis – about half of them seeking shelter with the UN.

Late on Tuesday the UN Security Council voted to increase its peacekeepers from 7,000 to 12,500, and its international police force from 900 to 1,323.

After the safe relocation of Americans from Bor, South Sudan, to the nation’s capital of Juba on Sunday, President Barack Obama said he may “take further action” to keep Americans safe in the midst of escalating violence and fears of possible civil war in the newly formed African country.

Three hundred and eighty U.S. officials and citizens have already been transported out of South Sudan in addition to 300 residents of other countries, Jen Psaki, the U.S. State Department‘s spokesperson, said in a statement.

Obama said in a letter that 46 U.S. military personnel were sent to Bor on Saturday in the evacuation effort.

“As I monitor the situation in South Sudan, I may take further action to support the security of U.S. citizens, personnel, and property, including our Embassy, in South Sudan,” Obama said.

“The U.S. government is doing everything possible to ensure the safety and security of United States citizens in South Sudan. … For their safety and security, we will not outline specific evacuation plans,” the statement said.

On Saturday, four U.S. service members were wounded when unidentified forces attacked three U.S. aircraft attempting to evacuate Americans from Bor. The involved aircraft and personnel aborted the mission and left the country, Obama said.

While the United Nations sends more peacekeeping soldiers into the violence-stricken country, all civilian officials who are involved with the U.N. Mission in the Republic of South Sudan (UNMISS) have been relocated to Jor, according to the U.N.

“We are not abandoning South Sudan. We are here to stay, and will carry on in our collective resolve to work with and for the people of South Sudan,” Special Representative for South Sudan and head of UNMISS Hilde Johnson said in a statement.

The decision came after a UNMISS camp was attacked by about 2,000 armed militants, leaving two Indian peacekeepers and “a number” of South Sudanese civilians dead, according to the U.N.

Violent clashes have escalated in the world’s newest country throughout the week, following what South Sudan’s President Salva Kiir’s government said was a coup attempted by rebels fighting for the former vice president who was dismissed in July.

U.N. Secretary-General Ban Ki-moon has called for the violence to stop immediately and for the disparate parties to “resolve their personal differences through dialogue immediately.”

US President Barack Obama warned the leaders of South Sudan against a military coup Saturday after four US servicemen were wounded in an attack on their aircraft in the increasingly unstable country.

“Any effort to seize power through the use of military force will result in the end of longstanding support from the United States and the international community,” the White House said in a statement.

Obama stressed that the South Sudanese leaders “have a responsibility to support our efforts to secure American personnel and citizens in Juba and Bor,” the capital and a rebel-held flashpoint town in the African nation.

The president’s comments came after three CV-22 Osprey aircraft came under fire in South Sudan as they headed to Bor to help with efforts to evacuate Americans from the country teetering on the brink of a return to civil war.

The attack damaged the tiltrotor aircraft, forcing them to divert to Uganda. The wounded were then flown to Nairobi for medical treatment and are now in “stable condition,” the Pentagon said in a statement.

The attack underlined the increasingly dangerous situation in South Sudan, where at least one UN base has also come under attack in recent days, with the murder of two Indian peacekeepers and possibly dozens of civilians.

The United States, Britain, Kenya and Uganda have been carrying out evacuation missions for their nationals.

Oil companies have flown out their workers after the death of at least five South Sudanese oil workers on Wednesday, with Chinese state oil company China National Petroleum Corpconfirming it was pulling out its staff.

Oil production accounts for more than 95 percent of South Sudan’s fledgling economy.

The United States has also deployed 45 combat-equipped troops to the country to protect its embassy and personnel.

The hostilities in the poor but oil-rich nation, which won independence from Sudan in 2011, are between troops loyal to President Salva Kiir and forces backing his sacked vice president, Riek Machar.

Kiir accuses Machar of having tried to mount a coup, but Machar denies that and claims Kiir is conducting a violent purge.

At least 500 people have been killed in the capital Juba alone in six days of fighting.

Foreigners evacuated, South Sudanese cower in fear

Tens of thousands have been displaced, many seeking shelter at UN bases amid warnings that the impoverished nation was on the brink of all-out civil war.

“I am afraid. I just can’t imagine being forced to become refugees again,” said Susan Nakiden, a South Sudanese woman among the thousands sheltering at a UN base in Juba. The mother of three said she had already been forced to flee her home during the civil war with Sudan.

Local resident John Luga said people were living in fear, whatever their clan.

“Whether they are Nuers or Dinkas, the suffering is for all, the future is not certain,” he told AFP.

South Sudan’s embattled government, meanwhile, said a top army commander in the northern Unity State, Major General James KoangChoul, had defected to Machar’s fast-growing rebel force.

“We have lost contact with the commander… and there are reports he has joined the forces of Riek Machar,” Sudan People’s Liberation Army spokesman Philip Aguer told AFP.

Army seeks to take back Bor

Aguer also insisted that government forces were in control of area around Bor, some 200 kilometers north of Juba, and an army operation was underway to take back the town seized by rebels this week.

“There is fighting, but we are supported by air units,” he said.

Although the unrest appeared to start as a result of a political spat, the violence has taken on an ethnic dimension pitting Kiir’s ethnic Dinkas against Nuers, to which Machar belongs.

South Sudan gained independence from Sudan as part of a peace process after a two-decade civil war that left two million dead, but it has never been able to heal its own ethnic rivalries.

US Secretary of State John Kerry underlined Obama’s message in a call to Kiir, telling him the conflict was threatening South Sudan’s hard-won independence that was backed by the United States.

Kerry has dispatched his special envoy for Sudan and South Sudan, Donald Booth, to the region to encourage talks between the warring factions.

African ministers have also stepped up pressure on Kiir to start talks with Machar.

United Nations Secretary-General Ban Ki-moon has called for an end to hostilities and urged the leaders of Sudan’s warring factions “to resolve their personal differences through dialogue immediately.”

Kiir has “apparently agreed to enter into unconditional dialogue,” Araud said after an emergency Security Council meeting on the crisis in South Sudan.

Meanwhile, UN Secretary GeneralBan Ki-moon again called for renewed peace efforts on Friday, amid rising concerns that heavy fighting between rival army factions is pushing the two-year-old nation into civil war.

“The secretary general reiterates his call for all parties to exercise restraint, and to cease hostilities,” said a statement from Ban’s office.

The UN chief urged opposition leaders “to demonstrate compromise and leadership on behalf of the Southern Sudanese people, and to resolve their personal differences through dialogue immediately.”

The fighting between troops loyal to Kiir, who is from the Dinka ethnic group, and opposition leader Riek Machar, a Nuer, erupted around Juba on December 15.

The South Sudanese president accused his arch-rival and former deputy, Machar, of attempting to topple his government, but he said the coup attempt had been foiled.

The government said on Tuesday that ten senior political figures had been arrested after the alleged coup attempt.

Machar has denied Kiir’s accusation that he had led a coup attempt.

South Sudan gained independence in July 2011 after its people overwhelmingly voted in a referendum for a split from the North.

The government in Juba is grappling with rampant corruption, unrest and conflict in the deeply impoverished but oil-rich nation, left devastated by decades of war.

At least 73 soldiers killed; UN urges sides to refrain from ethnic violence; US pulls out some embassy staff

Rival troops were locked in fresh battles in South Sudan’s capital on Tuesday in unrest that has killed at least 73 soldiers and sent thousands of terrified civilians fleeing since an alleged coup bid.

The fighting in the world’s youngest nation has set off alarm bells in the international community, with the United Nations urging the warring groups to refrain from ethnic violence.

President Salva Kiir on Monday accused soldiers loyal to his arch-rival, former vice president Riek Machar, of staging a coup attempt in the oil-rich but deeply impoverished nation.

A military hospital doctor said at least 73 soldiers have been killed in the fighting, which erupted late on Sunday in the capital Juba.

Sporadic clashes could be heard Tuesday in several parts of Juba, even though Kiir had announced that the city was under complete control.

The United States on Tuesday ordered all non-emergency embassy staff to leave South Sudan amid an eruption of fierce fighting, and urged all Americans to depart as well.

“The Department of State ordered the departure of non-emergency US government personnel from South Sudan because of ongoing political and social unrest,” it said in a statement, adding the mission in Juba would suspend normal operations for the time being.

Up to 13,000 people have fled to UN compounds to escape the clashes, UN chief Ban Ki-moon said Tuesday after talks with the country’s president.

Ban called on Kiir to make “an offer of dialog” to his opponents to end deadly fighting that erupted Sunday, said UN spokesman Martin Nesirky.

A top UN envoy said at least 10,000 civilians “have received protection in the two UNMISS compounds in Juba”, and that UN staff were “taking every possible step to ensure their safety”.

The special representative of the UN secretary-general, Hilde Johnson, said it was “paramount” that the conflict did not assume ethnic dimensions.

“At a time when unity among South Sudanese is more needed than ever, I call on the leaders of this new country and all political factions and parties, as well as community leaders to refrain from any action that fuels ethnic tensions and exacerbates violence,” she said in a statement.

The African Union also said it was “deeply concerned” about the events and urged all players to show “maximum restraint” and work towards a resolution.

The heavy fighting and the alleged coup has underscored the fragility of the nation which only became independent from Sudan in 2011.

Machar — who was sacked in July — leads a dissident group within South Sudan’s ruling party, the Sudan People’s Liberation Movement (SPLM), and had been seen as the main challenger to Kiir.

The two men hail from different ethnic groups and had in the past fought on different sides during Sudan’s long civil war.

South Sudan won its independence in July 2011 after its people voted overwhelmingly in a referendum to split from the north and form a new nation.

Awash with guns after the long war, the country has struggled with ethnic violence and corruption.

An aid worker with the British charity Oxfam, Emma Jane Drew, told AFP by telephone that the situation in Juba was “very tense”.

“It’s continued shooting. Shooting could be heard all through the night. We don’t know who is fighting who,” she said, adding her team was unable to leave their compound.

Communications down, airport closed

The independent radio station Tamazuj said clashes were taking place around compounds belonging to Machar or his loyalists.

Officials have said several former government ministers have been arrested, although the whereabouts of Machar is unclear.

“So far we have lost seven soldiers who died while they were waiting for medical attention and a further 59 who were killed outside,” military hospital doctor Ajak Bullen said on Miraya FM radio.

Another medical establishment, Juba Teaching Hospital, had earlier reported 26 dead, a mixture of civilians and military. It was not clear whether there was any overlap between the figures.

Military spokesman Philip Aguer declined to comment on the casualty figures, telling AFP only: “The soldiers are controlling the situation.”

Communications in Juba continued to be sporadic, with most phone lines down and the main airport closed, diplomats and civil aviation officials said.

An AFP reporter said residents living in areas close to military bases were using any lull in the fighting to flee for safer areas, although many said they were too afraid to move.

“We are afraid of going outside,” said Juba resident Jane Kiden. “We had wanted to go out and buy food from the market, but how can you go with the shooting? I am staying at home with my children.”

There were also unconfirmed reports of troops conducting violent house-to-house searches.

“We have heard unconfirmed reports of house-to-house military checks of civilians including the use of brutality and violence, though this is unconfirmed,” Oxfam’s Drew said.

The UN statement appeared to back up the reports by emphasizing the need for “discipline, command and control in the security forces”.